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The software upgrade brings a few new notable features to Apple's mobile devices, such as an improved Siri that's more contextual, a gorgeous News app, the addition of transportation directions in Apple Maps, and more.
And, if you've been holding on to your iPhone 4s for the past few years, here's some good news - older iPhones and iPads will support the new software too.
This is a new move for Apple; the company's new software typically runs more slowly on older phones.
But, since Apple has emphasized that it's focusing more on the "foundation" of iOS (i.e. security and performance) with iOS 9, it's taking steps to ensure the software works well on older iPhones and iPads too.
The oldest Apple devices that will run iOS 9 are the iPhone 4s and iPad 2, both of which were released in 2011.
Here are all of the iPhones, iPads, and iPod Touches that will support iOS 9 when it officially launches this fall:
Apple